Drill bit

ABSTRACT

A drill bit, the frame of which comprises a front section with protrusions. A set of first rear teeth is arranged at the front section, preferably at the rear part of the protrusions. The set of first rear teeth broadens a drilled hole when the drill is reversed.

[0001] The invention relates to a drill bit, the frame of which comprises a front section with protrusions.

[0002] A typical drill bit comprises a cylindrical frame with a front section, and the diameter of the front section is larger than the diameter of other parts of the frame. Such a drill bit is not guided properly; when the drill bit hits a hard rock slantwise, for example, it easily moves in the lateral direction and is stuck to the edges of a drilled hole. Furthermore, when such a drill bit is used, it is quite difficult to reverse the drill bit, i.e. pull the drill out of the hole. It is particularly difficult to reverse when drilling banks, for instance, whereby the material to be drilled is clay or a similar softish material and/or fragmental rock.

[0003] A drill bit for bank drilling is disclosed, the diameter of the drill bit being substantially the same both in the front section of the drill bit and in other parts of the drill bit. Further, rear teeth, i.e. a rear reamer, are arranged at the rear edge of the drill bit. The purpose of the rear reamer is to broaden a drilled hole when the drill is reversed. The material that is removed by the rear reamer from the edge of the hole, however, blocks up the area between the rear section and the front section of the drill bit fairly easily, and thus it is not always sufficiently easy to reverse.

[0004] It is an object of the present invention to provide a drill bit with very good properties.

[0005] The drill bit of the invention is characterized in that rear teeth are arranged in connection with the front section.

[0006] The essential idea of the invention is that a set of first rear teeth is arranged at the drill bit in connection with the front section of the drill bit. The idea of a preferred embodiment of the invention is that there are protrusions in connection with the front section such that the diameter of the front section measured at the protrusions is larger than the diameter of the middle section of the drill bit frame, and there are also protrusions in the rear section of the drill bit such that the diameter of the drill bit rear section measured at these protrusions is larger than the diameter of the middle section of the drill bit frame. The idea of another preferred embodiment is that the diameter of the drill bit rear section measured at its protrusions is smaller than the diameter of the drill bit front section measured at its protrusions. The idea of a third preferred embodiment is that a set of second rear teeth is arranged at the protrusions of the rear section of the drill bit.

[0007] The invention provides the advantage that the drill and the drill bit can be reversed quite smoothly and the gap between the drill bit and the hole does not block up easily. By arranging protrusions at the rear section of the drill bit, the drill bit is guided efficiently. By making the protrusions of the rear section smaller than the protrusions of the front section, guiding improves and also the gap between the rear section of the drill bit and the hole can be kept substantially unblocked during drilling and reversing. When a set of second rear teeth is arranged at the protrusions of the rear section, the set of second rear teeth of the rear section performs a pilot reaming during the reversing and the set of first rear teeth in the front section of the drill bit performs the actual reaming for the hole, which means that the reaming is performed in two stages and the reversing is implemented very smoothly and easily.

[0008] The invention is described in greater detail in the attached drawing in which

[0009]FIG. 1 schematically shows a side view of a drill bit according to the invention, partly in cross-section, and

[0010]FIG. 2 shows a front view of the drill bit according to FIG. 1.

[0011]FIG. 1 shows a drill bit 1. When the drill bit 1 is used, it is attached to one end of a drill rod by means of threads 2, for instance, or in some other manner known per se. The drill bit 1 comprises a front section 3, a middle section 4 and a rear section 5. Hard metal buttons 6 are arranged at the face of the drill bit frame in a manner known per se. Most preferably each hard metal button 6 is set above its own bulge in a manner shown in FIG. 2, whereupon flushing fluid can flow very efficiently and easily between the hard metal buttons 6 and the bulges. Protrusions 7 have been formed at the front section 3 such that the diameter of the front section 3 measured at the protrusions is larger than the diameter of the middle section 4. The drill bit 1 further comprises openings 8 which enable the flow of the flushing fluid.

[0012] A set of first rear teeth 9 is formed at the rear edge of the protrusions 7 in the front section 3. The first rear teeth 9 are slanting, as shown in FIG. 1, and when the drill bit 1 rotates in the direction shown by the arrow A, they broaden the drilled hole during the reversing of the drill bit 1 and thus facilitate the reversing. Since the set of first rear teeth 9 is in connection with the front section 3 of the drill bit 1, material that is removed by the set of first rear teeth 9 during the reversing easily flows past the front section 3 without blocking up the gap between the drill bit 1 and the wall of the drilled hole. Since the set of first rear teeth 9 is thus in connection with the front section 3, the distance between the set of first rear teeth 9 and the face of the drill bit 1 is rather short. The distance between the set of first rear teeth 9 and the face of the drill bit 1 is preferably shorter than the diameter of the front section 3 of the drill bit 1. It is particularly preferable that the distance between the set of first rear teeth 9 and the face of the drill bit 1 is so short that it is smaller than 0.5 times the diameter of the front section 3 of the drill bit 1.

[0013] A second set of protrusions 10 is arranged at the rear section 5 of the drill bit 1. The second set of protrusions 10 at the rear section 5 improves the guiding of the drill bit 1. However, the second protrusions 10 of the rear section 5 are lower than the protrusions 7 of the front section 3. Thus, the diameter of the rear section 5 measured at the second set of protrusions 10 is larger than the diameter of the middle section 4 of the drill bit 1, but smaller than the diameter of the drill bit 1 front section 3 measured at the protrusions 7. In this case, the gap between the rear section 5 of the drill bit 1 and the wall of the drilled hole does not block up very easily. A set of second rear teeth 11 is arranged at the rear end of the protrusions 10. When the drill bit 1 is reversed, the set of second rear teeth 11 performs a pilot reaming and the set of first rear teeth 9 in connection with the front section 3 functions as the actual reamer. The reaming is performed in two stages, whereby the drill bit 1 is reversed smoothly and the risk of blocking is eliminated.

[0014] The drawing and the related description are only intended to illustrate the idea of the invention. In its details the invention may vary within the scope of the claims. Consequently, the proportions between the front section 3, the middle section 4 and the rear section 5 may vary within fairly broad limits. Furthermore, the second set of protrusions 10 may at least partly extend to the middle section 4, for example. The second protrusions 10 at the rear section 5 may also be slanting or spiral. 

1. A drill bit, the frame of which comprises a front section with protrusions, the front section being provided with a set of first rear teeth, and a rear section which is provided with second protrusions which are arranged to improve guiding of the drill bit, the rear end of the second protrusions being provided with a set of second rear teeth.
 2. A drill bit as claimed in claim 1 , wherein the distance between the set of first rear teeth and the face of the drill bit is shorter than the diameter of the front section of the drill bit.
 3. A drill bit as claimed in claim 2 , wherein the distance between the set of first rear teeth and the face of the drill bit is smaller than 0.5 times the diameter of the front section of the drill bit.
 4. A drill bit as claimed in claim 1 , wherein the set of first rear teeth is arranged at the rear part of the protrusions.
 5. A drill bit as claimed in claim 1 , wherein the diameter of the drill bit front section measured at the protrusions is larger than the diameter of the other parts of the frame of the drill bit.
 6. A drill bit as claimed in claim 1 , wherein the drill bit comprises a middle section and a rear section and the rear section comprises a second set of protrusions such that the diameter of the rear section measured at the second set of protrusions is larger than the diameter of the middle section of the drill bit, but smaller than the diameter of the drill bit front section measured at the protrusions. 